Grain oriented electrical steel sheets, which are mainly used as iron cores of transformers, are required to have excellent magnetic properties, in particular, less iron loss.
To meet this requirement, it is important that secondary re-crystallized grains are highly aligned in the steel sheet in the (110)[001] orientation (or so-called the Goss orientation) and impurities in the product steel sheet are reduced. Additionally, there are limitations to control crystal orientation and reduce impurities in terms of balancing with manufacturing cost, and so on. Therefore, some techniques have been developed to introduce non-uniformity to the surfaces of a steel sheet in a physical manner and reducing the magnetic domain width for less iron loss, namely, magnetic domain refining techniques.
For example, JP 57-002252 B proposes a technique for reducing iron loss of a steel sheet by irradiating a final product steel sheet with laser, introducing a high dislocation density region to the surface layer of the steel sheet and reducing the magnetic domain width. JP 06-072266 B proposes a technique to control the magnetic domain width by electron beam irradiation.
However, when a grain oriented electrical steel sheet that has been subjected to the above-mentioned magnetic domain refining treatment is assembled into an actual transformer, it may produce significant noise.
It could therefore be helpful to provide a grain oriented electrical steel sheet that may exhibit excellent low noise and low iron loss properties when assembled as an actual transformer, along with an advantageous method for manufacturing the same.